1. Technical Field
The present disclosure relates to semiconductor manufacturing equipment, and more particularly, to a leveling algorithm for the semiconductor manufacturing equipment and a related apparatus.
2. Discussion of the Related Art
A process of manufacturing a semiconductor device includes a process of forming fine patterns on a semiconductor substrate, such as a silicon wafer. The process of forming the fine patterns may include a deposition process, a photoresist coating process, an exposure process, a development process, and an etching process. The exposure process includes transferring patterns to the photoresist using an exposure apparatus. A specialized technique is required for accurately transferring the patterns to exact positions of the photoresist for high integration of the semiconductor device. In addition, exposure apparatuses such as a scanner and a stepper widely employ a reduction projection exposure technique in which patterns formed on a reticle are reduced and transferred.
In general, the exposure apparatus has a light source, a condenser lens, a reticle, a projection lens, a wafer holder, and a leveling stage. A wafer coated with a photoresist is mounted on the wafer holder. Light transmitted through the reticle is projected onto the photoresist through the projection lens. The patterns formed on the reticle are transferred onto some regions of the photoresist on a field basis.
The surface of the photoresist should be positioned at the focal distance of the projection lens in order to accurately transfer the patterns. When the surface of the photoresist is closer or farther than the focal distance of the projection lens, patterning defects such as line thinning, end line shortening, and contact-not-open occur. The surface of the photoresist has different levels depending on the position, even on the same wafer. Accordingly, it is very important to read and control the surface level of the photoresist.
The leveling stage acts to adjust the wafer mounted on the wafer holder in up, down, right, left, front, back, and rotational directions. In order to effectively operate the leveling stage, the surface level of the photoresist should be accurately read.
FIGS. 1 and 2 are conceptual diagrams for explaining a conventional method of reading a surface level.
Referring to FIG. 1, a field F defined on a semiconductor substrate is aligned with a sensing apparatus SA. The field F has a plurality of chips that are arranged in a two-dimensional manner along rows R1, R2, and R3, and columns C1, C2, and C3. That is, the field F has a first chip R1C1 arranged in the first column C1 of the first row R1 to a ninth chip R3C3 arranged in the third column C3 of the third row R3. In addition, the field F has scribe lines SL disposed between the chips R1C1 to R3C3. The field F may be classified into a measurement-allowed region and a measurement-restricted region. Light reflected from the surface of the photoresist is influenced by the pattern or the structure within the field F. Accordingly, the measurement-allowed region is set to overlap within the chips R1C1 to R3C3, and the measurement-restricted region is set to include the scribe lines SL.
The sensing apparatus SA has a plurality of sensors S1, S2, S3, S4, S5, S6, S7, S8, and S9. Any of the sensors S1, S2, S3, S4, S5, S6, S7, S8, and S9 that overlap at least a part of the measurement-restricted region or that are out of the field F are turned off, and only those sensors that are completely within the measurement-allowed region are turned on.
Light is radiated onto the surface of the field F. Light reflected to the sensor S5 from the surface is sensed to generate a level signal. Radiating the light, sensing the reflected light, and generating the level signal are sequentially carried out while moving in the direction of an arrow 20.
The level signal is calculated to read the surface level of the field F. In this case, level signals are obtained from the fourth chip R1C2, the fifth chip R2C2, and the sixth chip R3C2 arranged in the second column C2. In contrast, level signals cannot be obtained from the first chip R1C1, the second chip R2C1, the third chip R3C1, the seventh chip R1C3, the eighth chip R2C3, and the ninth chip R3C3 arranged in the first and third columns C1 and C3. That is, the surface levels of the second column C2 of the field F can be read whereas the surface levels of the first and third columns C1 and C3 cannot be read. Accordingly, the directional inclinations of the rows R1, R2, R3 of the field F cannot be read.
Referring to FIG. 2, the field F may be positioned on an edge of the semiconductor substrate. An edge clearance EC is set on the edge of the semiconductor substrate. The edge clearance EC may be in contact with the third chip R3C1, the fourth chip R1C2, the fifth chip R2C2 and the sixth chip R3C2. In this case, the measurement-restricted region is set to include the scribe line SL, the edge clearance EC, and the chips R3C1, R1C2, R2C2, and R3C2 in contact with the edge clearance EC. However, according to the conventional method of reading the surface level, both of the sensors S3 and S4 corresponding to the first column C1 are turned off. As a result, the surface levels cannot be read from the first chip R1C1 and the second chip R2C1.
Consequently, according to the conventional method of reading the surface level, there are many regions where the surface level of the field F cannot be read, moreover surface level readings that can be obtained may be inaccurate.
Other methods associated with the conventional method of reading the surface level are disclosed in Japanese Patent Laid-Open Publication No. 2001-332471 entitled “Exposure Apparatus” to Hiroshi Kurosawa. According to Kurosawa, when a focus error is found at the edge of a wafer, an apparatus capable of carrying out a focused exposure is provided. However, the exposure apparatus may frequently produce inferior patterns.